Electronic systems, whether in telecommunications, data processing or other industries requiring operational capability at all times, necessitate the use of reserve power to accommodate the times when an AC power source outage occurs. This typically implies that a battery or a collection or "string" of batteries is required to supply the needed interim power. Often, the environment in which the batteries must operate provides harsh conditions that are extremely detrimental to them. Therefore, a battery monitoring system is typically used to monitor and condition them. The goal of the battery monitoring system is to protect the batteries from being damaged, provide a conditioning or recharging environment and ultimately extend useful battery life.
Parameters that are detrimental to batteries include: a large or uncontrolled charge current, a constant value of charging voltage that is too high, a high battery temperature that causes the battery to vent gas, shorted battery cells that force others to overcharge and conditions that overly discharge the battery. Conventional battery monitoring and conditioning systems are focused on simplicity of operation regardless of any degenerative impact that they may have on the batteries themselves. For example, a conventional battery monitoring and conditioning system may provide a single value of charging current during an initial phase of charging. This single value of charging current is typically maximized to assure that the batteries are charged quickly.
The maximum value of this current is often limited only by the internal resistance of the batteries themselves. A large value of battery charging current produces a high likelihood that the batteries will overheat. Overheating of the batteries causes their internal resistance to decrease further thereby allowing the charging current to further increase. This process, if unchecked, often produces a thermal runaway condition that either partially or severely damages the batteries. Even if the batteries do not enter a thermal runaway condition, a "thermal event" may exist wherein one or more of the batteries becomes overheated and vents gas to the environment causing those batteries to dry out over time.
After the batteries have reached a fully charged state under these conditions, the charge current is typically reduced in value, and the battery voltage usually decreases to a maintained value. Over time, battery cells that have been damaged by this charging process may become shorted. A shorted battery cell can no longer properly store energy, forces other batteries to overcharge and therefore usually requires that the battery or batteries be removed and discarded. Although simple in operation, this type of battery monitoring and conditioning system treats all batteries in the same way and usually monitors the voltage condition of the battery only to determine the presence of a shorted cell.
Accordingly, what is needed in the art is an improved way to monitor and condition batteries that avoids thermal events and allows the batteries to reach their full energy capacity.